When a downstream device connects to an upstream device using a single-uplink scheme, a single-point failure is prone to occur and results in service interruption. Therefore, a dual-uplink scheme is generally employed, that is, one downstream device concurrently connects to two upstream devices to avoid the single-point failure and improve network reliability. Though the dual-uplink scheme is capable of improving network reliability, a loop problem is introduced, and a loop needs to be eliminated using a loop-breaking protocol, such as the Spanning Tree Protocol (STP)/Multiple Spanning Tree Protocol (MSTP)/Rapid Spanning Tree Protocol (RSTP), the Rapid Ring Protection Protocol (RRPP), and the smart link (SmartLink) protocol.
However, when multiple downstream network devices are dual-linked to a same pair of upstream network devices, links to the pair of upstream network devices form multiple dual-uplink tangent rings. When virtual local area network (VLAN) deployment is per service per VLAN (PSPV), all links of the multiple dual-uplink tangent rings share one service VLAN. Though loop-breaking protocols can be deployed to prevent traffic from forming a loop in a broadcast domain, a fault in any dual-uplink tangent ring may cause a related entry of one or more other normal dual-uplink tangent rings to be cleared/updated and further cause traffic interruption, because the existing loop-breaking protocols clear/update a related entry on a VLAN basis. When there are a large number of users, many entry updates may be performed, which in turn leads to long-time service interruption.